This invention relates to industrial baghouses and, more particularly, to an improved method for cleaning the filter assemblies of baghouses.
Continuous emphasis on environmental quality has resulted in increasingly strenous regulatory controls on industrial emissions. One technique which has proven highly efficient in controlling air pollution has been the separation of undesirable particulate matter from a gas stream by fabric filtration.
Such filtration is carried out in dust collection apparatus known in the trade as a "baghouse" which operates on the same general principle as an ordinary household vacuum cleaner, except on a much larger scale. Basically, the baghouse is a sheet metal housing divided into two chambers, referred to as plenums, by one or more tube sheets. Disposed within openings communicating with the plenums are fabric filters. A particle-laden gas stream, induced by the action of a fan, blows into one chamber (dirty air plenum) wherein dust accumulates on the fabric filter as the gas passes through the fabric into the other chamber (clean air plenum) and out the exhaust.
Although all baghouses are designed in accordance with the foregoing general principles, there are numerous operational and structural distinctions. The present invention relates to a baghouse wherein the dirty and clean air plenums are separated by a tube sheet having a plurality of vertically suspended filter bags in which cylindrical wire cages are inserted for skeletal support. Filtration of the process gas occurs from outside to inside of the bags.
During continuous operation of the baghouse the bags must be periodically cleaned to remove the filter cake which accumulates on the fabric. One of two cleaning methods are typically employed in an outside bag collector. In pulsing-plenum cleaning, high pressure air is introduced to a compartment in the clean air plenum and the dust cake is simultaneously dislodged from all filter bags in that compartment. With pulse jet cleaning, on the other hand, the upper end of the cage is typically equipped with a diffuser, venturi or nozzle directed interiorly of the cage and a short blast of high pressure air is individually introduced through each nozzle. This pulse of air travels through the filter sleeve, causing it to flex out from the cage to dislodge the dust cake.
Further details of a baghouse having filter assemblies suspended from a tube sheet and employing pulse jet cleaning may be found in U.S. Pat. No. 3,876,402 by Bundy et al. issued Apr. 8, 1975, and specifically incorporated herein by reference.
It should be noted that either of the two foregoing cleaning methods (i.e. pulsing-plenum or pulse jet cleaning) are normally carried out without interrupting the flow of process gas. In other words, the baghouse continuously filters the particle-laden process gas stream at the same time some of the filter assemblies are being cleaned. The cleaning air is thus at a sufficiently high pressure to overcome the pressure of the process gas and back flush the filters to dislodge any dust cake. Consequently, complete shutdown of the baghouse is only necessary for maintenance and repair such as replacing defective filters.
To meet the needs for on-line maintenance and permit true 24 hour operation, industry developed a modularized baghouse made up of several filter modules filtering in parallel, each individual module itself being a complete baghouse. Since individual modules could be isolated for inspection and maintenance purposes while the majority of the modules were left in service, on-line baghouse maintenance became a reality.
Further details of a modularized baghouse may be found commonly assigned in U.S. Patent Application Ser. No. 765,989 by Bundy et al filed Feb. 7, 1977, and specifically incorporated herein by reference.
As an outgrowth of the development of modularized baghouses came recognition of the benefits which could be achieved by cleaning a isolated module. When cleaning a baghouse or module isolated and out of service, process gas flow is cut off which minimizes re-entrainment of dust particles and results in more efficient cleaning. Furthermore, there is a lower pressure drop to overcome in pulsing and there is far less damage to the bags when returning to their associated cages after flexure.
Contrary to industry practices, however, I have discovered that the foregoing advantages of isolated cleaning can be retained while achieving greater effectiveness and efficiency of cleaning the filter assemblies through incomplete isolation of the baghouse. Incomplete isolation is provided by establishing a pressure drop in the range of 1/4 to 11/2 inches water gauge in opposition to the cleaning air flow.
Accordingly, an object of this invention is to provide an improved baghouse cleaning method to maximize cleaning effectiveness and efficiency of the filter assemblies and at the same time minimize dust re-entrainment and bag damage.
Another object of the invention is to provide a baghouse cleaning method to insure maximum flexure of the filter bags on their associated support cages.
An additional object of the invention is to provide an improved cleaning method of the character disclosed equally suited to baghouses employing either pulsing-plenum or pulse jet cleaning cycles.
A further object of the invention is to provide suitable apparatus for practicing the cleaning method herein disclosed.
Other and further objects of the invention, together with the features of novelty appurtenant thereto will appear in the course of the following description of the drawing.